Concussions are traumatic brain injuries usually caused by a bump, blow, or jolt to the head that has the potential to affect normal brain function. It has been discovered that some concussions are caused by rotational velocities of the head and sudden decelerations of the brain. In addition, the numerous sub-concussive impacts that athletes are experiencing every day are leading to cognitive impairment. Some head injuries may initially appear to have no long-lasting effects, but current research is finding that many such injuries, such as concussions, may have serious, long-term effects. The likelihood of long-term effects may be further increased when one has experienced repeated head injuries or cumulative concussions.
The Head Injury Criterion (HIC) is often used to measure the likelihood of head injury arising from an impact. The HIC can be used to assess safety related to vehicles, personal protective gear, and sports equipment. HIC is typically defined by the formula shown below.
      H    ⁢                  ⁢    I    ⁢                  ⁢    C    =            {                                    [                                          1                                                      t                    2                                    -                                      t                    1                                                              ⁢                                                ∫                                      t                    1                                                        t                    2                                                  ⁢                                                      a                    ⁡                                          (                      t                      )                                                        ⁢                  dt                                                      ]                    2.5                ⁢                  (                                    t              2                        -                          t              1                                )                    }        max  
In this formula, t1 and t2 are the initial and final times (in seconds) of the interval during which HIC attains a maximum value, and acceleration is measured in g's (standard gravity acceleration). The maximum time duration of HIC, t2-t1, is limited to a specific value, usually 15 ms. Studies have found that concussions are found to occur at HIC=250 among athletes.
The Gadd Severity Index (SI) is another commonly used measure of the injury potential of an impact. SI is typically defined by the formula shown below.
      S    ⁢                  ⁢    I    =            ∫      0      T        ⁢                  a        2.5            ⁢      dt      
In this formula, a(t) is the acceleration-time pulse of the impact and T is the duration of the impact. This formula can be interpreted as the area under the acceleration time pulse, after the acceleration values have been exponentiated to the power 2.5. An SI score of 1000 approximates the limit of human tolerance. Impacts with an SI score higher than 1000 have a greater than zero probability of causing a life-threatening brain trauma.
In order to combat concussions and other head injuries in sporting activities, protective helmets are commonly worn whenever there is a possibility of injury to the head. For example, protective helmets are commonly worn in football, hockey, baseball, lacrosse, motor sports, extreme sports, and winter snow sports. Such helmets are intended to reduce the severity of impacts to the wearer's head and in some cases to reduce vibrations experienced by the wearer's head. Such helmets often do not sufficiently reduce impact severity and do not reduce vibrations. Moreover, such helmets often do not reduce rotational forces transmitted to the wearer's head during impact events.
Various test methods have been used to assess the impact performance of protective helmets. For example, U.S. Pat. No. 7,743,640 issued to Lampe describes a linear impact test method, where a weighted headform fitted with a helmet is propelled by a linear ram into another headform fitted with a helmet. Headform accelerations of the resulting impact are measured using accelerometers mounted within the headform. U.S. Pat. No. 6,871,525 issued to Withnall describes a method and apparatus for testing a football helmet using a weighted pendulum arm. A helmet is fitted onto a headform and the pendulum arm is raised and then dropped to impart an impact force upon the helmet. Headform accelerations resulting from the impact are measured using accelerometers mounted within the headform. U.S. Pat. No. 6,826,509 issued to Crisco describes a head mounted sensor system (HMSS) that can include a standard football helmet in which a plurality of accelerometers and a radio transmission device mounted. The instrumented helmet can be worn by players during practice and/or games. Accelerations sustained by a player's head can be measured using the in-helmet accelerometers. Acceleration data can then be transmitted to a radio receiving device and associated computing equipment providing “in vivo” acceleration data for helmet impacts sustained by a helmet wearer during practice and/or game play.
The publication “An Investigation of the NOCSAE Linear Impactor Test Method Based on In Vivo Measures of Head Impact Acceleration in American Football” (Journal of Biomechanical Engineering, Vol. 132, pp. 011006-1 to 011006-9) by Gwin provides a comparison between the linear impact test method and National Operating Committee for Standards in Athletic Equipment (NOCSAE) standard drop tests for Riddell Revolution helmets. Gwin further presents a correlation between linear impact testing and in-vivo data collected using in-helmet systems such as HMSS. Daniel presents in-vivo helmet impact statistics for youth, high school and collegiate players for that relate the number of impacts experienced during a season of play to the impact severity. The publication “Head Acceleration Measurements in Helmet-Helmet Impacts and the Youth Population” (MS Thesis, Virginia Polytechnic Institute and State University, Blacksburg Va., Apr. 16, 2012) by Daniel presents in vivo helmet impact statistics for youth, high school, and collegiate players for that relate the number of impacts experienced during a season of play to the impact severity. The publication “Analysis of Linear Head Accelerations From Collegiate Football Impacts” (MS Thesis, Virginia Polytechnic Institute and State University, Blacksburg Va., Apr. 22, 2005) by Manoogian presents similar in vivo statistics for collegiate players including a correlation between the number of impacts and resulting HIC. Manoogian presents HIC data for a group of nearly 10,000 hits, wherein the median HIC is 3.1.
Over the years, protective helmets have evolved with advances in technology. For example, U.S. Pat. No. 7,328,462 issued to Straus is directed to a protective helmet of the type used in football and has an external soft elastomer layer to absorb/dissipate some of the energy of an impact. Other features include a quick disconnect face guard, carbon fiber face guard with Kevlar wrap at junction points, a soft foam inner shell inside the intermediate hardened shell, and a head fitting structure including a plurality of pads, visco-elastic cells, and at least one inflatable bladder. In addition, the hardened shell may be formed as a lattice frame of strips having a plurality of fibers impregnated with resin. The resin may have a dye added that will indicate if and where an impact exceeding a predetermined value is incurred by the helmet to assist a physician in diagnosing a possible head trauma injury.
Strauss also developed a ProCap, worn by some players in the 1990's. The original ProCap was a tough polyurethane foam shell permanently attached to a standard hard helmet with Velcro.
U.S. Pat. No. 7,089,602 issued to Talluri is directed to a multi-layered, impact absorbing, modular helmet in which the preferred embodiment consists of two layers over the hard casing. The outermost layer consists of an air chamber ensconced within a highly durable polymeric material with one or more air pressure release valves.
U.S. Pat. No. 6,446,270 issued to Durr is directed to a sports helmet with an energy absorbent material such as vinyl nitrile sponge (VNS) being a combination of thermoplastic polyvinyl chloride and synthetic elastomer nitrile.
U.S. Pat. No. 4,287,613 issued to Schulz, U.S. Pat. No. 6,934,971 issued to Ide, and U.S. Pat. No. 7,240,376 issued to Ide describe prior-art football helmets. The publication “Change in Size and Impact Performance of Football Helmets from the 1970s to 2010” (Annals of Biomedical Engineering, Vol. 40, No. 1, January 2012, pp. 175-184) by Viano provides a comparison of prior-art football helmets, including differences in dimensions, construction, and impact performance.
U.S. Patent Application Publication No. 2011/0302700 filed by Vito et al. is directed to a vibration reducing headgear worn inside a helmet consisting of two layers of material.
U.S. Pat. No. 8,316,512 issued to Halldin describes a helmet with multiple hard shell layers that allow relative sliding between inner and outer hard shell layers.
Despite the use of protective helmets, concussions continue to occur in sports. In 2004, data collected from the head impact telemetry system used in the National Football League concussion studies found that 58 of 623 (9.8 percent) of professional football players who suffered a concussion also had a loss of consciousness.
Moreover, recent studies show that more than 62,000 concussions occur each year in high school sports, with football accounting for two of every three, according to the Brain Injury Association of Arizona. However, many more mild concussions likely go undiagnosed and unreported. Studies estimate that approximately 10 percent of all athletes involved in contact sports such as football have a concussion each year. In addition, close to 60 percent of concussions may go unreported because athletes are not aware of the signs and symptoms and do not think the injury is serious enough to report to medical personnel.
Failure to detect initial concussions may lead to compound concussions, which can cause second impact syndrome. Second impact syndrome is a condition in which a second concussion occurs before a first concussion has properly healed, causing rapid and severe brain swelling and often catastrophic results. Second impact syndrome can result from even a very mild concussion that occurs days or weeks after the initial concussion. Most cases of second impact syndrome have occurred in young athletes, particularly those who participate in sports such as baseball, football, hockey, and skiing. Second impact injury can occur within a matter of days or weeks, or even in the same game or competition if the athlete isn't removed and treated after the first concussion. Neither impact has to be severe for second impact syndrome to occur.
Several studies have shown a link between a history of brain injury and a higher probability of developing major depression later in life. Another study found that of 2,552 retired professional football players, over 11 percent of those with a history of multiple concussions also had a diagnosis of clinical depression. Players reporting three or more previous concussions were three times more likely to be diagnosed with depression than those with no history of concussion. Emerging research also shows cumulative damage and onset of Chronic Traumatic Encephalopathy after multiple concussions. Thus, there is risk that even lesser impacts can lead to long-term damage.
As a result of increased public awareness regarding concussions, sports leagues of all levels have updated their concussion policies. However, these policies typically only deal with treatment of players after a concussion has already occurred and do not address concussion prevention.
With advancements in athletic training methods and new workout supplements, today's athletes are bigger and stronger than ever, thereby increasing the potential for concussions. As a result, traditional protective helmets are no longer sufficient to protect against concussions. What is lacking in the art is a protective helmet to help combat the rise in concussions in sporting activities.